From 1986 till now I use an Alpha Fascination, freeride longboard. The board is 18.5 kg (41 lbs), 3.68m (145 inch) long, 67 cm (26 inch) wide. You can call it a dinosaur ;-) Does this make me a dinosaur too? Well, 44, so not yet ;-)

I only windsurf in south Spain (Mediterranean Sea) 5 weeks a year. The wind most of the time is 20 - 37 km/h (11 - 20 knots).

I think a Starboard Carve would be a nice replacement. But what size would be a good choice? 141, 131?
What I like: The look and shape. The footstraps positions can be placed more to the center for the first rides. I also want to be able to up-haul the sail.

What would be the best sail size for this board for winds in this range? 6.5 m2?

Gunther,
At your weight, and with 11-20 knots, I would suggest something smaller than the Carve 131 for your 6.5 m2 rig.
For that wind speed the Carve 111 would seem to me to be the best size for you.
If you get a larger rig (say 7.5m2) you could be planing on the Carve 111 in about 12 knots, and your 6.5 will get you planing in around 14-15 knots.
Roger

I hadn't thought about going smaller in board size like the Carve 111. I admit your proposition is tempting. But I won't be able to test these boards beforehand. Therefore I will play it safe and choose a little wider board for more stability. Seen your explanation (the smaller the better for my weight), I will probably choose the Carve 131.

I begin from zero again with my equipment. Can I buy only one sail for the wind range 11-20 knots? Or will I need 2 sails for not overpowering my arms in the upper range? (For the Carve 131)

Gunther,
Think about the Carve 121 then.
Yes, 2 sails (about 1 m2 apart) would be much better.
A 6.5 will not get your going on these boards in < about 14-15 knots.
A 7.5 will get you planing in about 12 knots, but will be too much sail
(hard on the arms) @ 16-17 knots.
Roger

Someone at Star-board called the Futura (=freerace board) the freeride board of the future. Would a Futura 121 be an option for me instead of a Carve 121? I never did a jibe in planing mode (it wasn't possible on the old board of 18.5 kg (41 lbs) with my sail). Will going from an old longboard (26 years) to a Futura be that more difficult compared to a Carve 121 that you wouldn't recommend it?

Are the same sails (6.5 and 7.5) correct for a Futura 121 for the same wind range (11 - 20 knots)?

Gunther,
Yes, the Futura 121 would be a good choice for you as well.
Speed potential is similar.
The Carve line may be a little easier to jibe, but since you haven't
yet learned to jibe, the learning curve would be about the same.
Yes, same sail sizes. Look for Free Race type sails as they have
significanlty more power and range than regular free ride sail designs.
Roger